$-3mn - 8n - p - 9 = 4n + 2p + 4$ Solve for $m$.
Solution: Combine constant terms on the right. $-3mn - 8n - p - {9} = 4n + 2p + {4}$ $-3mn - 8n - p = 4n + 2p + {13}$ Combine $p$ terms on the right. $-3mn - 8n - {p} = 4n + {2p} + 13$ $-3mn - 8n = 4n + {3p} + 13$ Combine $n$ terms on the right. $-3mn - {8n} = {4n} + 3p + 13$ $-3mn = {12n} + 3p + 13$ Isolate $m$ $-{3}m{n} = 12n + 3p + 13$ $m = \dfrac{ 12n + 3p + 13 }{ -{3n} }$ Swap the signs so the denominator isn't negative. $m = \dfrac{ -{12}n - {3}p - {13} }{ {3n} }$